A nanowire-based liquid biopsy method using cerebrospinal fluid cell-free DNA for targeted management of leptomeningeal carcinomatosis

Patients with EGFR-mutant NSCLC who progressed as LMC after 3rd-generation tyrosine kinase inhibitors (EGFR–TKIs) were evaluated. A nanowire-based cfDNA assay was performed for genotyping cfDNA from the CSF and plasma. We focused on de novo EGFR C797S mutation and MET amplification, which are the most common mechanisms of resistance to 3rd-generation EGFR–TKIs.

Among 11 patients, five (45.5%) had progression only at the leptomeninges. The tumor-associated CSF-cfDNA was identified in eight (72.7%) patients, and plasma-cfDNA in six (54.5%) patients. In the CSF-cfDNA, EGFR C797S mutation and MET amplification were detected in four (36.3%) and two (18.2%) patients, respectively. Of four patients with the C797S-positive LMC, only one had concurrent CSF-T790M mutation. Three patients who had the C797S-positive LMC without CSF-T790M mutation, received 1st–2nd generation EGFR–TKIs and showed clinical benefits for 20.8, 17.8, and 8.8 weeks, respectively. Serial assessment with cfDNA in these patients demonstrated that the CSF levels of C797S mutation were decreased with radiological or neurological improvement but the plasma levels of T790M mutation were markedly increased before objective progression.